The 100% utilized nodes which we were trying to balance to create space were those 20 nodes registered with racks /Example1 and /Example2.Thus based on following rack awareness rules in balancer (rule#3 for this issue) for block placement, it was not at all possible for even a single block to move compromising fault tolerance.

/** * Decide if the block is a good candidate to be moved from source to target.
* A block is a good candidate if
* 1. the block is not in the process of being moved/has not been moved;
* 2. the block does not have a replica on the target;
* 3. doing the move does not reduce the number of racks that the block has */

SOLUTION: Distribute nodes evenly across all racks.If this is not possible add additional storage to respective nodes OR add new datanodes to the respective racks.